Project Summary/Abstract The most effective treatment identified to date for severe mood and psychotic disorders is electroconvulsive therapy (ECT). These mental illnesses affect >6.5% of adults in the U.S. and account for a major proportion of disability in society. Despite its efficacy, the negative image of ECT drastically limits its use. Determining the mechanism by which ECT resolves severe psychiatric symptoms may facilitate the design of alternative therapies to engage these mechanisms without seizure and its perceived negative consequences. Towards this goal, this research team proposes to investigate overarching hypothesis that early growth response gene 3 (Egr3), which is activated by ECS, and orchestrates synaptic plasticity, memory, and regulation of growth factors, is a key mediator of therapeutic efficacy of ECS. The research team will test this theory by evaluating two complementary hypotheses. First, that Egr3 is required for ECT to regulate depression- related physiologic processes and to reverse depressive behavior. Second, that Egr3 upregulation is sufficient to reverse these brain and behavioral changes in the absence of seizure. This will be accomplished using innovative adeno-associated viral (AAV) constructs that express short hairpin RNAs to knock down Egr3, and scrambled RNA controls. Infusing these constructs into the ventral hippocampus (VH), a region critical for mood regulation, will allow determination of how Egr3 coordinates the response to ECS. In Specific Aim 1 this research team proposes to determine the roles of Egr3 in ECS-induced growth factor expression, neurogenesis, and dendritic sprouting in the hippocampus. In addition to AAV constructs, they will administer EdU (5-ethynyl-2'-deoxyuridine) to mark newly born neurons in the VH, followed by ECS vs. sham procedures. They will use immunohistochemistry to quantify VH neurogenesis and BDNF activation. Biocytin filling of AAV-positive neurons and adjacent controls will be used to determine the role of Egr3 in mediating the effect of ECS on the hippocampal neuron morphology and connectivity. In Specific Aim 2 this research team proposes to ascertain the necessity of Egr3 for the antidepressant effect of ECS on depression-like behavior in male and female mice. The team will use chronic mild stress to induce a depression-like state in mice, and test the requirement for Egr3 in the VH for the reversal of this state by ECS. Anti-depressant like response will be assessed using the validated forced swim test (FST). Knockdown of Egr3 is expected to abrogate the antidepressant-like effect of ECS on FST immobility. Moreover, to establish sufficiency of Egr3 to reduce depression-like behavior (i.e., even in the absence of seizure) they will infuse an Egr3 construct into the VH, which is expected to reduce immobility in the FST. The impact of this study will be the successful identification of the molecular mechanism for the efficacy of ECT. This will provide both fundamental insight into the neural dysfunction shared among mood and psychotic illnesses, as well as potentially reveal novel targets for next-generation therapies that do not require seizure.